With the growing number of remote local area networks (LANs) that require linking to central locations over wide area networks (WANs), and the ever-increasing demand for on-line services and data-intensive applications, there is a growing need for high bandwidth WAN access. Increasing bandwidth requirements and delay constraints imposed by real-time-interactive applications such as video conferencing, audio and video streaming, and basic telephony, dictate that WAN access maintain high levels of integrity.
To provide such integrity, asynchronous transfer mode (ATM) has become the technology of choice for maintaining integrity and reducing the complexity of WAN communications. ATM offers many benefits, including speed, scalability, traffic management, and the capability to combine LAN and WAN functions through a uniform protocol. Unfortunately, as enterprises require greater WAN access to support ever-increasing traffic loads, they are faced with either paying for very expensive T3 or E3 links that often go substantially unused, or adding additional T1 or E1 access lines, which often create multiple, parallel networks.
Inverse multiplexing over ATM (IMA) offers a solution to the above paradigm. IMA is a user-to-network interface standard approved by the ATM Forum in 1997, and specifies a transmission method in which ATM cells are distributed across multiple T1 or E1 lines, then reassembled at a terminating point while maintaining the original order of the ATM cells. By facilitating the transport of ATM cells over more cost-effective T1 and E1 lines, IMA facilitates the extension of ATM to areas having access to T1 or E1 lines. Thus, in situations where an application was limited to the 1.544 megabits per second provided by a T1 line, multiple T1 lines may be used to incrementally increase the unified traffic flow in a scalable fashion.
Unfortunately, IMA is data-focused, and does not incorporate the required redundancy for traditional telephone. Traditional telephone networks, such as the public switched telephone network (PSTN), require redundancy throughout the network and will not tolerate single points of failure. Thus, traditional telephony applications have not been able to take advantage of the bandwidth and scalability provided by IMA. Accordingly, there is a need for a way to provide redundancy in an IMA architecture to extend the benefits of IMA to voice telephony.